This invention relates to foam blowing agent blends containing trans-1,2-dichloroethylene (“Trans 12”) and one or more hydrofluorocarbons (“HFCs”), and to foam compositions containing such blends. Trans 12 is useful to improve the fire performance (that is, to suppress flame spread and smoke generation, as measured by ASTM E 1354 in terms of reduced rate of mass loss and reduced specific extinction area upon ignition) of HFC-blown, closed cell polymer (insulation) foams, such as polystyrene, phenolic and polyurethane foams.
Chlorofluorocarbons (“CFCs”) had been used as blowing agents for rigid, closed cell insulation foams for many years because they offer outstanding fire resistance in addition to good thermal insulation, since the CFCs are non-flammable. However, CFCs have been phased out because they are said to be detrimental to the ozone layer. Hydrochlorofluorocarbons (“HCFCs”) such as 1,1 -dichloro-1-fluoroethane (“HCFC-141b”) with low ozone depletion potential (“ODP”) have been alternatives for CFCs. However, HCFCs are also being phased out under the Montreal Protocol. The next generation of foam blowing agents must have zero ODP. For fluorochemical blowing agents, these are generally the HFCs such as 1,1,1,3,3-pentafluorobutane (“HFC-365mfc”). However, HFCs are typically more flammable than the CFCs or HCFCs, so that the new formulations will usually require higher levels of flame retardants in order to achieve the same levels of flammability. This increased level of flame retardant creates a problem because upon burning the flame retardants increase smoke levels. Thus, as disclosed by Albemarle Corporation in its website, Albemarle.com/saytexfr_polyurethane.htm, the addition of a brominated reactive polyol (RB-79) increases the smoke density of foam when subjected to fire tests. It has been reported that the use of 245fa alone will result in foams which generate high smoke density. What is thus needed is a means to achieve satisfactory blowing with HFCs while reducing the amount of fire retardant so as to reduce smoke density and lower overall cost. While Trans 12 has been disclosed as a foam blowing agent, as for example in U.S. Pat. No. 5,126,067, its use to reduce flame spread or smoke density has not been previously disclosed.